Deformation effects in toroidal and compression dipole excitations of $^{170}$Yb: Skyrme-RPA analysis

The effect of nuclear deformation on the isoscalar toroidal and compression dipole modes in prolate is studied in the framework of the random-phase-approximation method with a representative set of Skyrme forces (SV-bas, SLy6, and SkI3). It is shown that the deformation crucially redistributes the strength of both modes. The compression mode has the same sequence of and 1 branches as the isovector giant dipole resonance where for prolate nuclei the mode is lower in energy (μ being the projection of the axial momentum of the mode). Instead, the toroidal mode exhibits an unexpected (opposite) sequence where the branch precedes the one.